This invention relates to a method of manufacturing metallic slurry for casting. More precisely, it relates to a method of manufacturing metallic slurry for casting, including metallic slurry for Rheocasting and metallic slurry for casting billets for Thixocasting, which is a semi-solidified metallic slurry in which metal in a molten state (liquid phase) and metal in a solid state (solid phase) coexist and fine grains are mixed with liquid.
This kind of metallic slurry needs to be maintained in a state in which primary grains are separated from each other (by liquid matrix), and their crystal grains must be fine, homogeneous and non-dendritic, desirably globular. Slurry itself in such a state, or billet made by continuous casting and rapid cooling of the slurry and reheated becomes semi-molten metal of a high fraction solid and low viscosity, which can restrain shrinkage porosities in a casting and also improve its mechanical properties.
Various attempts have been offered for this reason.
A technique close to this invention was published in Japanese Patent Laid-Open No. Sho61-235047.
In the conventional technique, molten metal was poured on a temperature-controlled, inclined plate to produce a semi-molten metallic slurry as it flowed down the plate. However, the crystal grains became rosaceous and could not be satisfactorily globularized.
The object of this invention is to obtain metallic slurry for casting, particularly of aluminum alloys, and to offer a method of manufacturing such a slurry by which fine, homogeneous non-dendritic (globular) crystal grains can be obtained by means of simple facilities without requiring a complex process.
The method invented to achieve such an object is characterized by an arrangement to rapidly cool at least a portion of molten metal consisting of an aluminum alloy into a semi-solid state by putting the molten metal in contact with a cooling unit, and holding the molten metal within a semi-molten temperature zone for a given time. It is also characterized desirably by the adjustment of the temperature of the molten metal contacting the cooling unit between liquidus temperature TL and TL+60xc2x0 C., and also by the setting of the temperature of the molten metal at least a portion of which has been rapidly cooled into a semi-solid state between (TLxe2x88x92TS)/2+TS (TS represents solidus temperature) and TL+40xc2x0 C.
Further, it is characterized by an arrangement to make at least a portion of the molten metal contact a cooling unit by pouring and letting the molten flow on the cooling unit, which specifically is an inclined passage on which molten metal is poured and let to flow down, and the inclined passage is made in the shape of a plate, or gutter, or pipe.